In recent years laser generators have found wide use in both commercial and scientific applications. Lasers are sources of light and the light emitted by a laser has a number of unusual properties that distinguish it from light emitted by conventional light sources. Among the unusual properties are a high degree of collimation, a narrow spectral line width, good coherence, and the ability to focus to an extremely small spot. Because of these unusual properties, there are many possible applications for which lasers are suited. One such application is the laser engraving of a liquid transfer article such as a roll, used in the printing industry to transfer a specified amount of a liquid, such as ink or other substance, from the liquid transfer article to another surface. The printing roll is usually produced by laser engraving various size cells into portions of the roll surface. The cells are filled with a liquid and then the liquid is transferred to the receiving surface. The printing rolls are rather large and thus to laser engrave the surface of the rolls a fixed laser generator is employed which directs the laser beam onto a reflector carriage arranged to deflect the laser beam onto the surface of the roll. The roll is generally rotated while the reflector carriage is moved along the roll parallel to the longitudinal axis of the roll. In this manner, the roll can be laser engraved to provide any particular printing configuration.
One drawback in employing the above method of laser engraving is that with the movement of the reflector carriage along the roll, fine line effects have been produced in repetitive bands along the length of the roll when using a CO.sub.2 laser source. The bands have been found to occur at intervals of approximately 200 mm and within each band the lines occur at 2.8 mm spacing. Although the lines are visible on the roll and sometimes may effect the printed product, there appears to be no apparent difference in the geometry of the engraved cells in the surface of the roll. In addition to the line effect that has been observed, it is well known that control of beam diameter and divergence are essential to achieve consistent engraving along the length of a roll. This is of particular importance with respect to coarse engraved products such as applicator rolls.
Robotic arm devices have been disclosed in the art for use with laser generating means to produce a constant laser beam length for treating different areas of a workpiece. Although, the use of robotic arms can produce a constant laser beam length for treating various workpieces, it generally results in altering the polarization of the laser. In addition, the robotic arm is a rather complex device that could be quite expensive to make.
It is an object of the present invention to provide a device that can be used with a laser generating source to produce a constant laser beam length for treating various size and shape workpieces.
It is another object of the present invention to provide a device that can be used with a fixed laser generator to produce a constant laser beam length for laser engraving a workpiece such as a printing roll.
It is another object of the present invention to provide a device for use with a laser generator that can provide a constant laser beam length for laser treating workpieces that is cost effective to produce and easy to make.
It is another object of the present invention to provide a method for laser treating various workpieces from a fixed laser generator source while maintaining the length of the laser beam constant.
The above and further objects and advantages of this invention will become apparent upon consideration of the following description thereof.